1. Cellular Wireless Networks
Many people use wireless communication devices (WCDs), such as cell phones, computers, laptop computers, and personal digital assistants (PDAs), to communicate with cellular wireless networks. Service providers that operate these wireless networks typically distribute WCDs to their subscribers, perhaps by selling the WCDs at retail outlets or over the Internet, or perhaps by offering WCDs at no cost to people that subscribe to a particular service plan.
Service providers then typically assign each WCD a telephone directory number—often known as a mobile identification number (MIN) or mobile directory number (MDN)—under which a WCD may operate. Via a manual or over-the-air provisioning process, the service provider will cause the WCD to store its MIN in its Number Assignment Module (NAM). Furthermore, a WCD is typically provided at the time of manufacture with an electronic serial number (ESN), which identifies the WCD as a unique physical device.
These WCDs and networks typically communicate with each other over a radio frequency (RF) air interface according to a wireless protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more industry specifications such as IS-95 and IS-2000. Wireless networks that operate according to these specifications are often referred to as “1×RTT networks” (or “1× networks” for short), which stands for “Single Carrier Radio Transmission Technology.” Another protocol that may be used is known as Evolution Data Optimized (EV-DO), perhaps in conformance with one or more industry specifications such as IS-856. Other protocols may be used as well, such as Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA), WiMax, and/or any others.
These networks typically provide services such as voice, Short Message Service (SMS) messaging, and packet-data communication, among others, and typically include a plurality of base stations, each of which provide one or more coverage areas, such as cells and sectors. When a WCD is positioned in one of these coverage areas, it can communicate over the air interface with the base station, and in turn over one or more circuit-switched and/or packet-switched signaling and/or transport networks to which the base station provides access.
The base stations for these networks are typically not associated with any subscriber or small group of subscribers in particular; rather, they are placed in publicly-accessible locations and are used by the service provider's customers generally. These base stations collectively blanket large geographic areas with coverage; as such, they are referred to generally and herein as “macro (or macro-network) base stations” and the network they collectively form—or to which they collectively belong—is referred to generally and herein as the “macro network.”
WCDs and macro base stations conduct communication sessions (e.g., voice calls and data sessions) over frequencies known as carriers, each of which may actually be a pair of frequencies, with the base station transmitting to the WCD on one of the frequencies, and the WCD transmitting to the base station on the other. This approach is known as frequency division duplex (FDD). The base-station-to-WCD link is known as the forward link, while the WCD-to-base-station link is known as the reverse link.
Either or both of the forward link and the reverse link may be further divided based on Time Division Multiplexing (TDM) in which a plurality of time-divided channels are provided on the link, or based on Code Division Multiplexing (CDM) in which a plurality of code-divided channels are provided on the link. The use of TDM to provide services between an infrastructure node (e.g., base station) and a plurality of client nodes (e.g., WCDs) is generally referred to herein as TDMA. The use of CDM to provide services between an infrastructure node and a plurality of client nodes is generally referred to herein as CDMA.
WCDs are programmed to use a pre-determined algorithm to select one of the carriers to use in communications with a base station. When a WCD is not engaged in an active communication session, the WCD does what is known as idling on the selected carrier, which means among other things that the WCD is tuned to that carrier for receiving page messages, SMS messages, and other similar messages, and that the WCD will also send access requests for call origination and other purposes to the base station on that carrier.
2. Femtocells
Many macro-network subscribers, including private consumers and businesses, among others, in addition to having wireless service (which may include data service) for their WCD (or WCDs), also have high-speed (a.k.a. “broadband”) Internet access through another communication channel. This other channel may be cable-modem service, digital-subscriber-line (DSL) service, satellite-based Internet service, T1 service, and/or some other option.
In an example arrangement, a user may have a cable modem connected (a) via coaxial cable to a cable provider's network and (b) via Ethernet cable to a local wireless network (e.g., IEEE 802.11 Wi-Fi-enabled router). The router may include one or more Ethernet ports to which additional computers or other devices may also be connected, and may include wireless-access-point functionality, providing a Wi-Fi packet-data interface to, for example, laptop computers, digital video recorders (DVRs), appliances, and/or any other computing devices or wireless network adapters.
To address gaps in macro-network coverage (e.g., in buildings and homes) and for other reasons, macro-network service providers have recently begun offering their clients devices referred to herein as femtocells.
A typical femtocell may be approximately the size of a desktop phone or Wi-Fi access point, and is functionally a low-power, low-capacity version of a macro base station. Thus, a typical femtocell will use a normal power outlet, perhaps with a transformer providing a DC power supply. The femtocell may have a wired (e.g., Ethernet) or wireless (e.g., Wi-Fi) connection with the user's router and/or cable modem, and would thus have connectivity to the Internet and/or one or more other packet-data networks via the user's broadband connection. The femtocell may then also have access to the devices connected to the user's router through the router's Ethernet and/or Wi-Fi interfaces.
A femtocell may establish a virtual-private-network (VPN) connection over the Internet with an entity (e.g., a VPN terminator) on the wireless-service (macro-network) provider's core network, and thereby be able to securely communicate with the VPN terminator and other entities on that core network and beyond. The femtocell may thus provide additional functionality to WCDs that it serves via access to the core network.
The femtocell also has a wireless-communication (e.g., CDMA, TDMA) interface that is compatible with the user's WCD(s), such that the femtocell may act as a micro base station, providing local wireless coverage on the wireless-service provider's network via the user's Internet connection. Usually, a femtocell will provide service on a single RF carrier (or on a single carrier per technology, where multiple technologies (such as CDMA and TDMA) are supported), and also transmit what is known as a pilot beacon, which includes administrative messages and parameters that WCDs can use to connect with the femtocell.
In particular, the pilot beacon identifies one or more of the carriers and/or channels at the femtocell that the femtocell is providing service on, and on which a pilot may be found. The femtocell's pilot may serve as a demodulation reference and handoff-level-measurement signal, among other purposes. While in some protocols, such as CDMA, the pilot is provided on a separate CDMA channel, other protocols, such as EV-DO (which, among other aspects of the protocol, utilizes TDMA concepts on the forward link), interlace the pilot in time slots among those used to transmit user traffic.
Femtocells may also include a location-determination module (e.g., some combination of hardware, firmware, and/or software). As an example, the location-determination module may comprise a Global Positioning System (GPS) receiver for receiving and decoding GPS signals for use in determination of location, as well as for use in synchronizing operations with other femtocells and with the macro network based on timing information embedded in the GPS signals. Other location-determination methods could also be used. In some instances, a femtocell may not have any location-determination module or capability.